docs: def P_stagnation(P, T, Tst, k):
      r'''Calculates stagnation flow pressure `Pst` for a fluid with the
      given isentropic coefficient and specified stagnation temperature and
      normal temperature. Normally used with converging/diverging nozzles.
  
      .. math::
          \frac{P_0}{P}=\left(\frac{T_0}{T}\right)^{\frac{k}{k-1}}
  
      Parameters
      ----------
      P : float
          Normal pressure of a fluid [Pa]
      T : float
          Normal temperature of a fluid [K]
      Tst : float
          Stagnation temperature of a fluid moving at a certain velocity [K]
      k : float
          Isentropic coefficient []
  
      Returns
      -------
      Pst : float
          Stagnation pressure of a fluid moving at a certain velocity [Pa]
  
      Notes
      -----
      Assumes isentropic flow.
  
      Examples
      --------
      Example 12-1 in [1]_.
  
      >>> P_stagnation(54050., 255.7, 286.8, 1.4)
      80772.80495900588
  
      References
      ----------
      .. [1] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
         Applications. Boston: McGraw Hill Higher Education, 2006.
      '''
      return P*(Tst/T)**(k/(k - 1.0))